Several factors are known to increase the risk of developing NIDDM, including a family history of diabetes, previous history of gestational diabetes (GDM), obesity, decreased physical activity, presence of impaired glucose tolerance (IGT) or insulin resistance. Moreover, the incidence of NIDDM is higher in several racial and ethnic minority groups in the US including African Americans, Hispanics, Native Americans, Native Alaskans, and Asian Americans. A five year multicenter trial is proposed to evaluate intervention strategies to prevent or delay the progression of IGT to NIDDM, or the progression of previously undiagnosed NIDDM with normal fasting glucose to fasting hyperglycemia. Within the context of the overall study design, the Joslin Diabetes Center, (JDC) South Cove Community Health Center (SCCHC) and Brigham and Women's Hospital (BWH) will collaborate to form a participating clinical center and will identify a cohort of 200 high risk patients (equal to approximately 100 patients with IGT or previously undiagnosed NIDDM and 100 obese women with a previous history of GDM) to be prospectively and randomly assigned to one of four intervention groups, comprising a 2 x 2 factorial design. Half of the patients will receive standard diet and exercise recommendations (standard group), while half will receive an intensive lifestyle modification program, including individualized dietary and exercise programs, instruction in behavioral change, stress reduction, smoking cessation and close follow up (intensive group). Within each group, half will be randomized to treatment with low dose sulfonylurea, and half will receive placebo. Volunteers will be screened and recruited from specifically identified high risk populations. These include first degree relatives of patients with NIDDM at the JDC, first degree relatives of patients with NIDDM at the SCCHC, first degree relatives of patients with NIDDM in the Harvard Community Health Plan and patients with a past history of obesity and GDM at BWH.